Thermal pump and process

ABSTRACT

Thermal pump and process for pumping gases by contacting a gas of relatively low pressure and low temperature with one face of a non-porous permeable membrane supported on both faces by rigid porous material, passing the gas through the membrane by means of solution therein, evaporating gas from solution in said membrane at the other face of said membrane, the evaporated gas being at a higher temperature and higher pressure than before its passage through the membrane, heat-exchange means being placed on both sides of the membrane.

NOV. 23, 1971 MQKADAM 3,621,665

THERMAL PUMP AND PROCESS Filed Nov. 28, 1969 HEAT IN FIG. I

F HEAT EXCHANGER EVAPORATOR TH ROTTLE HEAT IN (LOAD) 4 f E HVV/zfi. I w-RAGHUNATH G. MOKADAM ATT'YS United States Patent 3,621,665 THERMAL PUMPAND PRQCESS Raghunath G. Mokadam, Chicago, Ill, assignor to American GasAssociation, Arlington, Va. Filed Nov. 28, 1969, Ser. No. 889,732 lint.Cl. 182% 7/00 U5. Cl. 612-49 15 Claims ABSTRACT OF THE DISCLOSUREThermal pump and process for pumping gases by contacting a gas ofrelatively low pressure and low temperature with one face of anon-porous permeable membrane supported on both faces by rigid porousmaterial, passing the gas through the membrane by means of solutiontherein, evaporating gas from solution in said membrane at the otherface of said membrane, the evaporated gas being at a higher temperatureand higher pressure than before its passage through the membrane,heat-exchange means being placed on both sides of the membrane.

Compressors and pumps of the prior art move gas from a low pressure areato a high pressure area by mechanical means. Typically, rotary,reciprocating or other types of pumps having many moving parts are used.Pumps with moving parts are subject to mechanical breakdown for variousreasons including wear and general lack of upkeep. Another problemcommon to pumps and compressors having moving parts is noise. Theseproblems have been particularly severe in compressors and pumps used incooling devices, which often require continuous operation over longperiods of time.

In my invention, the above problems associated with pumps having manymoving parts have been eliminated by use of a novel thermal pump andprocess which can compress a gas without the use of moving parts.Specifically, a gas is moved from an area of lower pressure to an areaof higher pressure by passing through a nonporous permeable membrane bymeans of solution.

My invention requires no moving parts to accomplish its pumping action.Therefore, there is no chance of mechanical breakdown due to wearbetween moving parts. Also, there can be no noise.

Some permeable membranes having one face exposed to a particularrelatively low pressure and low temperature gas will allow passagetherethrough by means of solution of the gas in the membrane andsubsequent evaporation of the gas at the other face of the membrane,which is exposed to the same gas at a relatively higher temperature andhigher pressure. If a suitable cooler and a suitable heater are placedproximate to the low temperature and high temperature faces,respectively, gas will continue to move from the low pressure side ofthe membrane to the high pressure side, entering the membrane by meansof exothermic solution at the membrane face on the low temperature side,moving in solution through the membrane, and evaporating at the membraneface near the high pressure and high temperature side as heat isprovided by the heater.

The terms low and high, when used to modify pressure or temperature areused in a relative sense herein, that is, relating the gas conditions onopposing sides of the membrane. This invention is operable over wideranges of pressure and temperature, limited only by the use intended andby structural and operational factors.

It is one object of this invention to provide a pump and process forpumping which overcomes many problems of pumps of the prior art.

It is another object of this invention to provide a pump ic 11 fl.

and process for pumping requiring substantially no moving parts.

It is a further object of this invention to provide a thermal pump andprocess for pumping which moves gas by means of solution with anon-porous permeable membrane.

Yet another object of this invention is to provide a pump and processfor pumping which is substantially free of noise.

Still another object of this invention is to provide a thermal pump andprocess for pumping which can be used in a wide variety of pumping andcompressing applications including with cooling devices.

Another object of my invention is to provide a thermal pump and processfor pumping using a non-porous permeable membrane having the samematerial on both faces thereof.

These and other important objects will become apparent from thefollowing description and from the drawings showing preferred embodimentwherein:

FIG. 1 is a partial cutaway plan view of a thermal pump of thisinvention.

FIG. 2 is a schematic drawing of a cooling system using a thermal pumpof this invention.

Referring specifically to FIG. 1 a thermal pump of this invention isshown having container 25 defining passageway 26, inlet passage 2,outlet passage 16, inlet thermal exchanger 4, outlet thermal exchanger15, fins 3 on both of the thermal exchangers, permeable membrane 6having membrane first face 10 and membrane second face 11, first porousstructure 5 having first porous structure first face 8 and first porousstructure second face 9, and second porous structure 7 having secondporous structure first face 12 and second porous structure second face13. The permeable membrane extends across passageway 26 and withcontainer 25 defines inlet passage 2 and outlet passage 16.

A gas enters thermal pump inlet passage 2 at A at a temperature of T anda pressure of P The same gas may be in outlet passage 16 at atemperature of T higher than T and pressure of P higher than P The gasin inlet passage 2 passes through first porous structure 5, contactsmembrane first face 10 and goes into solution with permeable membrane 6at membrane first face '10. As the gas goes into solution, the heat ofsolution is absorbed by inlet thermal exchanger 4, said inlet thermalexchanger being proximate to first porous structure 5 and therefore alsoto membrane first face 10. Inlet thermal exchanger 4 may also absorbsome sensible heat of the gas and heat which is conducted through themembrane from high temperature outlet passage 16. I

The dissolved gas flows in solution through permeable membrane 6. Asheat is provided by outlet thermal exchanger 15, the dissolved gasevaporates from solution in the permeable membrane at membrane secondface 11. Besides absorbing heat which becomes the heat of solution, thegas absorbs additional heat from the outlet thermal exchanger. The gas,at pressure P greater than P and temperature T greater than T exitsthermal pump outlet passage 16 at B. The thermal pump may serve to movegas or to increase gas pressure in a reservoir.

The theory of gas flow in solution with a non-porous permeable membraneis not completely understood. I have observed that the volume of gasflow is related to the pressure gradient across the membrane. Arelatively large pressure gradient across a. permeable membranegenerally will cause a relatively high rate of gas flow in solution fromthe high pressure to the low pressure side. A relatively large thermalgradient across a permeable membrane will generally cause a relativelyhigh rate of flow from the low temperature side to the high temperatureside. The effect of a high thermal gradient can overcome the effect of apressure gradient and thus allow flow of gas from low pressure and lowtemperature side to high pressure and high temperature side. In thethermal pump and process of this invention, a relatively high thermalgradient and a relatively low pressure gradient are preferred.Specifically, a thermal gradient high enough to overcome gas flow insolution caused by the existing pressure gradient is required. As thepressure gradient becomes large, its effect on gas flow in solution willovercome the effect of the large thermal gradient. Thus, if the thermalpump is being used as a compressor to raise the pressure of a gas in thereservoir, its effectiveness will diminish as the pressure gradientbecomes too large with respect to a given thermal gradient. Therefore,there is a practical limit to the high pressures which may be achieved.The relative solubility of a gas in a membrane at the differing pressureand temperature conditions and the resultant concentrations of solutionat the membrane faces are probably important factors in gas flow insolution with a non-porous permeable membrane. 1 have found that theflow rate varies inversely with the level of pressure of the system,temperatures and temperature gradient being constant.

Referring specifically to FIG. 2, a cooling system is shown havingthermal pump 1 of FIG. 1, condenser, heat exchanger, throttle andevaporator. The thermal pump of this cooling system replaces the motordriven compressor, or the absorber and generator of an absorptionsystem. It is a source of compressed gas. The outlet thermal exchangerprovides heat to maintain the desired high thermal gradient between theinlet passage and the outlet passage. After passing through the thermalpump and exiting at B, the gas has pressure P and temperature T Itenters the condenser and leaves as liquid at pressure P and temperatureT T is lower than T and P is substantially the same as P The cooling andchange of phase occurs because of heat rejection in the condenser. Thecondensed liquid is cooled in the heat exchanger to temperature Tpressure P being substantially the same as R The condensed liquid isthen throttled to relatively low pressure P and relatively lowtemperature T.,. The liquid then enters the evaporator where itevaporates upon picking up the heat load. The pressure P, isapproximately the same as P and temperature T is approximately the sameas T Then the gas passes through the heat exchanger, its temperatureincreasing to T P being substantially the same as Pf- The porousstructures referred to above offer only negligible resistance to gasflow. Gas may enter first porous structure 5 at first porous structurefirst face 8 and exit second porous structure 7 at second porousstructure second face 13 with substantial freedom. The porous structuresprovide support for permeable membrane 6, which is placed between saidporous structures, membrane first face 10 being against first porousstructure second face 9 and membrane second face 11 being against secondporous structure first face 12. The material used for porous structuresmay be any material which would provide adequate support for themembrane and allow substantially free passage of gas. Another importantfactor to be considered in choosing material for the porous structuresis conductivity. It is highly preferable that the porous structures havea high thermal conductivity to enable adequate passage of heat both toand from the nonporous permeable membrane. Preferred materials arehighly porous to allow substantially free passage of gas, strong and ofeven texture to provide rigid support for the membrane, and of a highconductivity. Examples of preferred materials are porous ceramic andporous metallic pieces. Especially preferred materials are porousbronze, steel and copper. The thickness may vary widely, theconsiderations being degree of support, passage of gas and conduction ofheat; Durability and corrosion re .4 4 sistance are other factors to beconsidered in choosing a material for the porous structures.

The permeable membrane of this invention must be of a material which canserve as a solvent for the gas being used. The membrane must benon-porous, that is, gas must not be allowed to pass therethrough freeof solution. It is also necessary that the solubility of the gas in themembrane be higher at the lower pressure and temperature conditionswhich will be used than at the higher pressure and temperatureconditions. It is highly preferred that the membrane have a low thermalconductivity; lower conductivity will provide higher efiiciency in thethermal pump as a high thermal gradient is more easily maintained. Themembrane must be chosen in reference to the gas to be used and viceversa.

The thickness of the membrane may vary over wide ranges, keeping in mindthat thinness favors gas passage and thickness allows less undesiredheat conduction. These factors must be balanced. A preferred range isfrom .001 to .010 inch. I have found in my work that approximately .002inch is a favorable thickness for natural rubber latex. The membraneface area may vary over a large range, depending upon configuration,capacity and requirement of associated apparatus.

Although the membrane will normally be made of one material and havethat material on both faces thereof, by ganging several membrane layersa larger thermal gradient may be obtained across the membrane. Thepermeable membrane may be laminated, and may contain differentmaterials.

Any gas which cannot be condensed at the desired operating conditionswithin the thermal pump and will be dissolved in the permeable membranebeing used is suitable for this invention. If the thermal pump is to beused in a cooling application as in FIG. 2, the gas must be such that itwill condense at the proper pressure and temperature conditions.

As previously mentioned, the gas must be chosen in view of the choice ofpermeable membrane. A preferred combination of gas and permeablemembrane is carbon dioxide with natural rubber latex. Especiallypreferred combinations are Freon 11, Freon 12 and Freon 22 with naturalrubber latex. Freon designates a group of halogenated hydrocarbonscontaining one or more fluorine atoms which are used as refrigerants.

The container for the thermal pump may be made in a wide variety ofshapes and sizes. The container must be substantially airtight except asindicated at A and B. The container may be made of any material whichwould serve as support for the various components set forth. It ispreferred that the container be made of material of low thermalconductivity. Suitable material would be apparent to one skilled in theart and familiar with the invention. Similarly the heat sink heatexchanger, cooler, conduits connecting the components of the system, andthe pumps as indicated are standard in the art and would be apparent toone familiar with this invention.

The inlet and outlet thermal exchangers extend across the inlet andoutlet passages, respectively, passing in airtight fashion through thecontainer and providing thermal communication from and to said thermalpump. Gas in the inlet and outlet passages may pass the inlet and outletthermal exchangers substantially freely in heat-exchange relation.

The inlet and outlet thermal exchangers may be of widely varying types.Any thermal exchanger which may be used to transfer heat from one fluidto another is suitable. Tubes with fins are preferred. It is preferredthat fins be made of a highly thermal-conducting porous metal. Sinteredstainless steel 60% dense is especially preferred. Copper surfaces arealso preferred. The use of a porous type metal will promote thermalexchange between the contained gas and the inlet and outlet thermalexchangers.

The thermal pump and process of this invention may be used in manydifferent applications requiring movement of gases. Its advantages, asaforementioned, are not limited to any particular application. The pumpand process may be used for wide varieties of refrigeration applicationsincluding air-conditioning. Thus the heat load of FIG. 2 would come fromair in the space to be cooled. The thermal pump and process may also beused in many chemical processes. This invention may be used in movingvery low temperature gases. There is particular advantage possible inthis area because large thermal gradients are more easily attainable.Numerous other specific applications would be apparent to one skilled inthe art and familiar with this invention.

EXAMPLE Pressure Tempera- (p.s.i.a.) ture F.)

The thermal pump in this system replaces the compressor or absorber andgenerator in cooling systems from the prior art. The apparatus andprocess, as shown in this example, provide a suitable cooling system.

While in the foregoing specification this invention has been describedin relation to certain preferred embodiments thereof, and many detailshave been set forth for purpose of illustration, it will be apparent tothose skilled in the art that the invention is susceptible to additionalembodiments and that certain of the details described herein can bevaried considerably without departing from the basic principles of theinvention.

Iclaim:

1. A process for the thermal pumping of gas comprising the steps ofpassing a low pressure and low temperature gas in heatexchange relationto an inlet thermal exchanger, said inlet thermal exchanger cooling saidgas and a membrane first face of a non-porous permeable membrane,

contacting said gas with said permeable membrane at said membrane firstface, said gas being capable of solution in said permeable membrane andsaid membrane not permitting substantial passage of gas therethroughexcept by means of solution,

passing said gas through said permeable membrane by solution of said gasinto solution with said permeable membrane at said membrane first face,movement of said dissolved gas within said permeable membrane to amembrane second face of said permeable membrane and evaporation of saiddissolved gas from said permeable membrane at said membrane second faceupon heating of said membrane second face by an outlet thermalexchanger, said gas evaporated from said membrane second face havinghigh pressure and high temperature, and said gas having lower solubilityin said membrane at said high pressure and high temperature than at saidlow pressure and low temperature, and

passing said gas in heat-exchange relation to said outlet thermalexchanger, said outlet thermal exchanger heating said gas.

2. The process of claim 1 wherein said permeable membrane is of onematerial.

3. The process of claim 1 wherein said permeable membrane has severalmembrane layers.

4. The process of claim 1 wherein said gas is Freon 22 and saidpermeable membrane is natural rubber latex.

5. The process of claim 1 wherein said gas is Freon 22.

6. The process of claim 1 wherein said gas is a Freon.

7. The process of claim 1 wherein said permeable membrane is naturalrubber latex.

8. A thermal pump comprising a container defining a passageway, saidpassageway being divided by a nonporous permeable membrane extendingthereacross, said container and said permeable membrane defining aninlet passage and an outlet passage such that a gas may not freely flowfrom one passage to the other, said permeable membrane permittingsubstantial passage of gas therethrough only by means of solution, saidpermeable membrane having a membrane first face and a membrane secondface, an inlet thermal exchanger being proximate to said membrane firstface, an outlet thermal exchanger being proximate to said membranesecond face, said thermal exchangers providing thermal communicationfrom and to said thermal pump.

9. The thermal pump of claim 8, said non-porous permeable membrane beingsupported by a first porous structure, said first porous structurehaving a first porous structure second face against said membrane firstface of said permeable membrane and providing support for said permeablemembrane, and a second porous structure, said second porous structurehaving a second porous structure first face against said membrane secondface and providing support for said permeable membrane.

10. The thermal pump of claim 9 wherein said permeable membrane is ofone material.

11. The thermal pump of claim 9 wherein said permeable membrane hasseveral membrane layers.

12. The thermal pump of claim 9 wherein said gas is Freon 22 and saidpermeable membrane is natural rubber latex.

13. The thermal pump of claim 9 wherein said gas is Freon 22.

14. The thermal pump of claim 9 wherein said gas is a Freon.

15. The thermal pump of claim 9 wherein said permeable membrane isnatural rubber latex.

References Cited UNITED STATES PATENTS 2,182,098 5/1939 Sellew 62-11'6 X3,407,622 10/1968 Turnblade 62-498 3,407,626 10/1968 Turnblade 62-498WILLIAM J. WYE, Primary Examiner US. Cl. X.R.

